The Advanced Encryption Standard (AES) is a symmetric key encryption algorithm that operates on 128-bit blocks of data and uses a key size of 128, 192, or 256 bits. It uses a substitution-permutation network (SPN) structure, where the input block is divided into columns and each column undergoes a series of transformations using a round key derived from the main key. AES uses a combination of substitution, permutation, and mixing operations to produce the ciphertext, making it much more secure than its predecessor, the Data Encryption Standard (DES). AES is widely used in various applications, including online banking, file encryption, and secure communications.